This invention relates to a process for recovering useful water and other materials from a water containing mixture found in oil field mud and waste pits typically containing solids, hydrocarbons and aqueous chemical impurities and the apparatus for practicing the process. During the drilling of oil wells and the production of oil from subterranean formations, large quantities of water are used which become contaminated with the components of drilling mud, tailings removed from the hole during drilling operations, hydrocarbons from the producing formation, and large quantities of salts, both naturally occurring and added to drilling fluids during drilling operations. As the search for oil goes deeper and more remote from sources of water, the value of useful water increases, particularly in situations where it is necessary to move water by truck to well sites to provide water needed for drilling operations.
Further, the proper disposal of oil well drilling fluids deposited in waste pits presents serious environmental and ecological problems. The practice of dumping water from oil well operations containing both brine, solids, in the form of sand and minerals, and hydrocarbons, into unlined earthen pits on the surface dates back to the early 1920's. Heretofore, such waste fluids have typically been allowed to accumulate in open pits with the water being allowed to evaporate and the residual salts and solids simply retained in the pit. However, this practice has been found to constitute a major source of pollution to underground fresh water tables through the leaching of contaminates through the earth into the water table. Each rainfall that occurs causes the deposited salts and other soluble chemicals to leach from the pits and ultimately to be carried into the underground water table. Salt contamination, principally sodium and potassium chlorides, may render the water in such tables unfit for human and animal consumption or as irrigation water for agricultural use.
Present methods for treating oil field waste pits do not allow for recovery of usable water or of dissolved and dispersed oil. Ecologically safe disposal has necessitated either the hauling of the waste to safe disposal sites or the expensive rendering of the waste to becoming environmentally safe. With rapid increase in oil drilling operations, waste pits become an ever increasing economic and environmental problem. To avoid costly cleanup operations, some pits are cut to dump contaminates into surrounding areas and others are allowed to stand until evaporation of water permits them to be buried. This still does not solve the problem of leaching caused by rainfall.
Several methods have been disclosed relating to the treatment of mud/waste pits but all fall short of a method for economically producing reusable and, in many cases, even potable water. A method described in U.S. Pat. No. 3,764,008 for example, describes the separation of oil well production fluids which include water, liquid hydrocarbons and oily sand through the use of additional water for cleaning oil from the sand and separating sand from the liquid and then floating the oil from the water. This neither takes care of salts dissolved in the water nor of dispersed hydrocarbons. Another method for separating oil, particulate solids and water is described in U.S. Pat. No. 3,574,329. The treatment of well drilling mud is described in U.S. Pat. Nos. 2,886,287 and 2,919,898 for recovering usable drilling mud and recycling it through the system but not for recovering water itself from such systems. Desalinization of water through the use of a reverse osmosis system is well known and described in U.S. Pat. Nos. 3,821,108 and 4,161,445 for example. These patents teach the recovery of relatively useful water to begin with and do not relate to the recovery of usable or even potable water from a mud/waste pit. One system described in an Oil and Gas Journal article (Dec. 1, 1980 at pages 138 and 139) involves chemical treatment and, in extreme situations, clarifiers and centrifuges to recover usable water from pits which are not salt contaminated. Most mud/waste pits are contaminated with salt. Other than for this last reference, and it falls far short as set forth above, none of the references mentioned above even attempt to solve the problem solved by the invention described herein.
The practice of the present invention provides a relatively inexpensive method for cleaning oil field mud/waste pits or production fluids such that the search for hydrocarbon reserves and the production thereof is accomplished in an economical and environmentally beneficial way.
Although the primary focus of this invention is to the recovery of usable water from oil field mud/waste pits, numerous other applications will be apparent to those skilled in the art from the disclosure which follows.